Endeavors have been made for many years to manufacture asphalt shingles having appearances of natural materials, such as slate, tile, and cedar shakes.
In the course of manufacture of such shingles, it is known to use a mat, generally of fiberglass construction, impregnated with an asphalt or other bitumen material, and then to apply granules to the shingle, to adhere to the bitumen material.
When shingles are to be laid-up on a roof, with each successive course overlying in part, an underlying course of shingles, it is generally not considered necessary that the same granules be applied both to the butt (or headlap) region of the shingle as will be applied to the tab region of the shingle, because the butt region of the shingle will be covered by one or more next-overlying shingles, whereas the tab region of a shingle will remain visible.
Consequently, when decorative granules are to be applied to a shingle, they are generally only applied to a tab region, because that is the region of the shingle that will be visible when the shingle is laid-up on a roof.
Various techniques have been developed for making the tab regions of shingles decorative, often to resemble natural materials, as mentioned above.
Often, different decorative effects are sought to be applied to different tabs of the same multi-tab manufactured shingle, such that each tab can simulate an individual tile, piece of slate, cedar shake, etc.